85 research outputs found
EURHINODELPHINIDS FROM THE EARLY MIOCENE OF PERU: FIRST UNAMBIGUOUS RECORDS OF THESE HYPER-LONGIROSTRINE DOLPHINS OUTSIDE THE NORTH ATLANTIC REALM
Among the many hyper-longirostrine dolphins (Odontoceti) from the Miocene, members of the family Eurhinodelphinidae bear two highly distinctive cranial features: a long and edentulous premaxillary portion of the rostrum and a mandible that is significantly shorter than the rostrum. Until now, unambiguously attributed members of this clade were only recorded from early to middle Miocene deposits of the North Atlantic realm (east coast U.S.A., North Sea Basin, and Mediterranean). In this work we describe and compare two partial skulls of longirostrine dolphins from late early Miocene (Burdigalian, 19.25-18 Ma) marine deposits of the Chilcatay Formation, in the East Pisco Basin (southern coast of Peru), preserving rostral and mandibular material, as well as ear bones. Based on these specimens we report diagnostic remains attributable to this family for the first time for the whole Southern Hemisphere and the whole Pacific Ocean. This major expansion of eurhinodelphinids' palaeogeographic distribution contrasts with their proposed shallow-water, coastal environments; it suggests a new dispersal route for members of the family across the Central American Seaway; and it further highlights the similarities between the odontocete faunas of the southeastern Pacific and North Atlantic realm during the Miocene. Better-preserved eurhinodelphinid specimens from the odontocete-rich Chilcatay Formation will allow for a more detailed comparison with North Atlantic members of the family
A well preserved skeleton of the fossil shark Cosmopolitodus hastalis from the late Miocene of Peru, featuring fish remains as fossilized stomach contents
Both the preservation of the poorly mineralized skeleton of sharks and the preservation of stomach contents are rarely observed in the fossil record. Here we report on a partial skeleton of a lamniform shark, including portions of the visceral arches and the anterior segment of the vertebral column, collected from the late Miocene beds of the Pisco Formation exposed at Cerro Yesera (Ica Desert, South Peru). Based on the morphology of the preserved teeth, this specimen was determined as a juvenile of the extinct lamnid species Cosmopolitodus hastalis. The shark skeleton includes remains of fish (featuring a pilchard determined as Sardinops sp. cf. S. sagax) in the abdominal region. These fish remains are interpreted herein as the fossilized stomach contents of the shark. For the first time, piscivory is demonstrated in a juvenile individual of Cosmopolitodus hastalis. This result is consistent with the current knowledge about the feeding habits of immature individuals of extant lamniform shark species (including Carcharodon carcharias and Isurus oxyrinchus). Our report further outlines the fundamental role of schooling pilchards in the late Miocene trophic chains of the highly productive coastal waters off present South Peru. Moreover, the find of this well preserved shark skeleton strengthens the qualification of the Pisco Formation as a Fossil-Lagerstätte, and emphasizes the role of early mineralization processes in cases of exceptional preservation
A new large squalodelphinid (Cetacea, Odontoceti) from Peru sheds light on the early miocene platanistoid disparity and ecology
The South Asian river dolphin (Platanista gangetica) is the only extant survivor of the large clade Platanistoidea, having a well-diversified fossil record from the Late Oligocene to the Middle Miocene. Based on a partial skeleton collected from the Chilcatay Formation (Chilcatay Fm; southern coast of Peru), we report here a new squalodelphinid genus and species, Macrosqualodelphis ukupachai. A volcanic ash layer, sampled near the fossil, yielded the 40Ar/39Ar age of 18.78±0.08Ma (Burdigalian, EarlyMiocene). The phylogenetic analysis places Macrosqualodelphis as the earliest branching squalodelphinid. Combined with several cranial and dental features, the large body size (estimated body length of 3.5 m) of this odontocete suggests that it consumed larger prey than the other members of its family. Together with Huaridelphis raimondii and Notocetus vanbenedeni, both also found in the Chilcatay Fm, this new squalodelphinid further demonstrates the peculiar local diversity of the family along the southeastern Pacific coast, possibly related to their partition into different dietary niches. At a wider geographical scale, the morphological and ecological diversity of squalodelphinids confirms the major role played by platanistoids during the EarlyMiocene radiation of crown odontocetes
How whales used to filter: exceptionally preserved baleen in a Miocene cetotheriid
Baleen is a comb-like structure that enables mysticete whales to bulk feed on vast quantities of small prey, and
ultimately allowed them to become the largest animals on Earth. Because baleen rarely fossilises, extremely
little is known about its evolution, structure and function outside the living families. Here we describe, for the
first time, the exceptionally preserved baleen apparatus of an entirely extinct mysticete morphotype: the Late
Miocene cetotheriid, Piscobalaena nana, from the Pisco Formation of Peru. The baleen plates of P. nana are
closely spaced and built around relatively dense, fine tubules, as in the enigmatic pygmy right whale, Caperea
marginata. Phosphatisation of the intertubular horn, but not the tubules themselves, suggests in vivo
intertubular calcification. The size of the rack matches the distribution of nutrient foramina on the palate, and
implies the presence of an unusually large subrostral gap. Overall, the baleen morphology of Piscobalaena
likely reflects the interacting effects of size, function and phylogeny, and reveals a previously unknown degree
of complexity in modern mysticete feeding evolution
Inside baleen: Exceptional microstructure preservation in a late Miocene whale skeleton from Peru
Exceptionally preserved delicate baleen microstructures have been found in association with the skeleton of a late Miocene balaenopteroid whale in a dolomite concretion of the Pisco Formation, Peru. Microanalytical data (scanning electron microscopy, electron probe microanalysis, X-ray diffraction) on fossil baleen are provided and the results are discussed in terms of their taphonomic and paleoecological implications. Baleen fossilization modes at this site include molding of plates and tubules, and phosphatization. A rapid formation of the concretion was fundamental for fossilization. We suggest that the whale foundered in a soft sediment chemically favorable to rapid dolomite precipitation, allowing the preservation of delicate structures. Morphometric considerations on the baleen plates and bristles coupled with the reconstructed calcification of the latter permit speculation on the trophic preferences of this balaenopteroid whale: the densely spaced plates and the fine and calcified bristles provide evidence for feeding on small-sized plankton, as does the modern sei whale
A new platyrostrine sperm whale from the Early Miocene of the southeastern Pacific (East Pisco Basin, Peru) supports affinities with the southwestern Atlantic cetacean fauna
Contrasting with their suction feeding modern relatives in the families Kogiidae and Physeteridae, Miocene physeteroids display a broad range of feeding strategies. Despite the continuous improvements of the fossil record, the transition from the earliest sperm whales to suction feeding forms as well as the once prominent macroraptorial forms remains poorly understood. In the present work, we investigate a partial sperm whale skull from Lower Miocene (Burdigalian) strata of the Chilcatay Formation of the East Pisco Basin, along the southern coast of Peru. Based on this specimen, we describe a new species in the genus Diaphorocetus Ameghino, 1894, which was previously known only by the holotype of Diaphorocetus poucheti (Moreno, 1892) from a roughly synchronous unit in Patagonia (Argentina). Differing from the latter in its smaller cranial dimensions, higher tooth count, and minor differences in the position of facial foramina, the new species Diaphorocetus ortegai n. sp. confirms a key character of D. poucheti, the marked dorsoventral flattening of the maxillary portion of the rostrum. Such cranial proportions suggest that, compared to other physeteroids, D. poucheti and D. ortegai n. sp. were more efficient at performing fast lateral sweeps of their rostra to capture small- to medium-sized prey items with their proportionally
small teeth. Recovered as stem physeteroids in our phylogenetic analysis, these sister species contribute to the ecomorphological disparity of sperm whales during the Early Miocene, but without displaying any of the cranial and dental changes occurring in later, macroraptorial and suction feeding sperm whales. The description of a new species of Diaphorocetus from southern Peru increases the similarities between the toothed whale faunas from the local Chilcatay Formation and the Gaiman and Monte Leon formations of Argentinian Patagonia, pointing not only to dispersal routes between the southeastern Pacific and southwestern Atlantic during the Burdigalian, but also to relatively similar ecological settings along the
coasts of Peru and Patagonia at that time
Looking for the key to preservation of fossil marine vertebrates in the Pisco Formation of Peru: new insights from a small dolphin skeleton
The upper Neogene Pisco Formation of Peru is known worldwide as one of the most significant Cenozoic
marine vertebrate Konservatt-Lagerstätten, even featuring cetacean specimens that retain remains of soft tissues or
stomach contents. Previous works showed that biomediated precipitation of dolomite concretions around large-sized
decaying carcasses was one of the most relevant processes responsible for exceptional fossil preservation. In turn, little is
known about the modes of fossilization of well-preserved small-sized vertebrates, which are rather common in the Pisco
Formation, but mostly do not exhibit dolomite concretions. We report on a cetacean specimen, identified as belonging
to the extinct short-snouted, small dolphin species Brachydelphis mazeasi (Pontoporiidae), preserved within a late
Miocene sandy deposit at the site of Pampa Corre Viento. This specimen consists of a moderately disarticulated partial
skeleton exhibiting well-mineralized bones; it is not enclosed within a dolomite concretion, being however delimited
by an evident dark boundary in the host sediment. Scanning electron microscopy and microanalytical investigations
identify Mn-oxides and apatite as early diagenetic minerals around the skeleton. We argue that a rapid burial of the
specimen was pivotal for the preservation of the bones, and allowed the early establishment of anoxic processes for
degradation of organic matter. Coupled with availability of P in porewater, the reducing conditions and the lowered
pH allowed precipitation of Ca-phosphate while increasing Mn solubility close to the pontoporiid carcass. Mn-oxides
precipitated at the redox boundary, the latter defining the outer edge of the volume of sediment affected by altered
chemical conditions due to the decaying processes. The permeability of the sediment and the small size of the carcass
were possible factors unfavorable to extensive sulfate reduction, thus preventing the formation of a dolomite concretion
and allowing bone phosphatization. This record emphasizes the role of conditions favorable to bone mineralization in
absence of an isolating carbonate concretion, in cases of high quality preservation of small-sized vertebrates observed
in the Pisco Formation. The observation of patterns in the distribution of diagenetic minerals in the sediment enclosing
vertebrate remains without, or with limited carbonate concretions provides insights into early taphonomic processes
A rhinopristiform sawfish (Genus pristis) from the middle eocene (lutetian) of southern Peru and its regional implications
Modern sawfishes (Rhinopristiformes: Pristidae) are circumglobally distributed in warm waters and are common in proximal marine and even freshwater habitats. The fossil record of modern pristid genera (i.e., Pristis and Anoxypristis) dates back to the early Eocene and is mostly represented by isolated rostral spines and oral teeth, with phosphatised rostra representing exceptional occurrences. Here, we report on a partial pristid rostrum, exhibiting several articulated rostral spines, from middle Eocene strata of the Paracas Formation (Yumaque Member) exposed in the southern Peruvian East Pisco Basin. This finely preserved specimen shows anatomical structures that are unlikely to leave a fossil record, e.g., the paracentral grooves that extend along the ventral surface of the rostrum. Based on the morphology of the rostral spines, this fossil sawfish is here identified as belonging to Pristis. To our knowledge, this discovery represents the geologically oldest known occurrence of Pristidae from the Pacific Coast of South America. Although the fossil record of pristids from the East Pisco Basin spans from the middle Eocene to the late Miocene, sawfishes are no longer present in the modern cool, upwelling-influenced coastal waters of southern Peru. Given the ecological preferences of the extant members of Pristis, the occurrence of this genus in the Paracas deposits suggests that middle Eocene nearshore waters in southern Peru were warmer than today. The eventual disappearance of pristids from the coastal waters off southern Peru might be interpreted as reflecting the late Cenozoic trend of strengthening of the Humboldt Current
Insights into the diagenetic environment of fossil marine vertebrates of the Pisco Formation (late Miocene, Peru) from mineralogical and Sr-isotope data
The late Miocene Pisco Formation of Peru is an outstanding example of richness and high-quality
preservation of fossil marine vertebrates. In order to reconstruct the fossilization path, we present
new textural, mineralogical and Sr-isotope data of diagenetic minerals formed in correspondence of fossil
specimens such as marine vertebrates and mollusks. These fossil specimens were found at Cerro los
Quesos, in the Ica Desert, within the diatomaceous strata of the Pisco Formation. Dolomite, gypsum,
anhydrite and Mn minerals are the main phases found, while the calcium carbonate originally forming
the mollusk valves is replaced by gypsum. An early formation of dolomite and of Mn minerals, triggered
by the modifications of the geochemical environment due to organic matter degradation, is suggested by
the textural relationships and is confirmed by the Sr isotopic ratio of dolomite, which agrees with that of
seawater at the time of sedimentation. Instead, gypsum Sr isotopic ratios indicate a pre-Miocene
seawater-derived brine circulating within the sedimentary sequence as a source for Sr. Oxidation of
diagenetic sulfide causing a lowering of the pH of porewater is proposed as an explanation for Cacarbonate
dissolution. The diagenetic chemical environment was, nevertheless, favorable to bone
preservation
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